The present invention relates to a preliminary ventilating device for vehicles which employs, for example, solar battery and storage battery which are used as an auxiliary and a main power sources, respectively.
Japanese Patent Publication No. 51451/1984 discloses a vehicle in which parking ventilation is performed, i.e., the interior thereof is ventilated while the vehicle is parked, by a ventilation fan serving as ventilation means which is driven by the electromotive force from a solar battery. In such a vehicle which employs a solar battery, the power generated by the solar battery is efficiently used as a power source for charging the vehicle's storage battery while the vehicle's engine is operating and, hence, a dynamo thereof is generating a sufficient amount of power, or when the temperature of the outdoor is low and, hence, the aforementioned parking ventilation is not necessary.
Japanese Patent Laid-Open No. 172016 discloses a ventilation systm for vehicles to eliminate an excessive increase in the temperature of the interior of the vehicle which occurs when the vehicle has been parked for a long time under a scorching sun in summer time, because it makes a driver or passenger uncomfortable when they get in the vehicle and it takes some time for an air conditioner to lower the temperature to a comofortable level. In Japanese Patent Laid-Open No. 172016, a ventilation fan, serving as ventilation means, automatically operated when the temperature of the interior of the parked vehicle reaches a predetermined value or above, is provided, and parking ventilation is performed, i.e., the air in the interior of the vehicle is replaced with fresh air, by the operation of such a ventilation fan. This ventilation fan is driven by the solar battery which sends out an output voltage corresponding to the amount of sunlight it receives.
In a vehicle which employs both the chargeable storage battery and the solar cell arrays and in which the storage battery is charged from the solar battery, a switch must be provided to open and close a charging circuit for charging the storage battery, and this switch must be adequately controlled in accordance with changes in the voltage of the storage battery, i.e., in response to the necessity of charging of the storage battery.
More specifically, it is possible to connect the solar battery to the storage battery through the switch, and to control the switch so that it breaks the connection between the solar battery and the storage battery when it is determined that the voltage of the storage battery reaches the reference voltage. However, when the switch is turned off and supply of power from the solar battery is stopped, discharge current of the solar battery does not flow and the open-circuit voltage thereof thereby increases to about 20 volts, which is higher than the voltage of the storage battery which is 12 volts.
When the voltage of the solar battery is measured in its open-circuit state, the increase to about 20 volts in the open-circuit voltage is detected. As a result, even when the storage battery discharges and the voltage thereof thereby drops and charging of the storage battery from the solar battery is thus made possible, the storage battery may not be able to be charged from the solar battery.
In the aforementioned vehicle which employs as the power source of the ventilating fan the solar battery characterized by the generation of a voltage corresponding to the amount of sunlight it receives, when a predetermined amount of sunlight cannot be obtained, the ventilating fan may not be able to be driven. Therefore, it has been proposed to determine whether or not a sufficient amount of power for activating the ventilating fan is sent from the solar battery, and to activate the ventilating fan on the basis of the results of the determination. However, individual solar battery arrays differ greatly from each other in output voltage. Also, a d.c. motor for driving the ventilating fan requires a large current when a relatively low voltage is applied thereto.
Last two factors will now be described in more detail with reference to FIG. 15 which shows the relationship between activation characteristic curve R of a d.c. motor, reference voltage current curve X of a reference solar battery, and voltage current curve Y of an individual solar battery. In FIG. 15, reference voltage current curve X, indicated by the broken line, ensures that all the d.c. motors for the ventilating fans can be activated when the voltage and current of the solar battery are applied to the d.c. motors at a predetermined amount of sunlight. In other words, when the voltage and current of the solar battery are applied, all the d.c. motors can be activated, if the voltage current curve of that solar battery exceeds the lower first peak RA which appears on the activation characteristic curve R. The conventional motor activating method does not cause any problem, if all the solar batteries manufactured exhibit characteristics equivalent to reference voltage current curve X.
However, there exist solar batteries exhibiting voltage current curve Y, which is lower than reference voltage current curve X, at the same amount of sunlight as that assuring reference voltage current curve X. When such a solar battery is used, the d.c. motors cannot be activated, because voltage current curve Y does not exceed the first peak RA of activation characteristic curve R. Hence, it is possible to measure a difference .DELTA.V between the open-circuit voltage of reference voltage curve curve X and that of voltage current curve Y beforehand and to activate the motors when the amount of sunlight is increased and when voltage current curve Y2, which assures generation of an open-circuit voltage higher than that of reference voltage current curve X by .DELTA.V and which is higher than the activation characteristic curve R, can thus be obtained.
When the solar battery exhibits voltage current curve Y2, it generates an electromotive force of, for example, 50 mW/cm.sup.2 at the maximum amount of sunlight. This means that the solar battery cannot be used in a state where it exhibits voltage current curve Y1 assuring activation of the ventilating fans, indicated by the alternate long and short dash line in FIG. 15, e.g., when it generates an electromotive force which is higher than 30 mW/cm.sup.2 by 5 mW/cm.sup.2.
In other words, in a solar battery exhibiting voltage current curve Y which is lower than reference voltage current curve X, variations in the voltage are great when the voltage is measured in an open-circuit state, and voltage measurement errors of .DELTA.V thus occur when the open-circuit voltage thereof is measured in an open-circuit state in which it is not connected to a load. Hence, the motors cannot be activated unless the amount of sunlight received by the solar battery is at a maximum.